This application claims priority of Taiwanese application no. 092201759, filed on Jan. 29, 2003.
1. Field of the Invention
The invention relates to a power tool, more particularly to a power tool having a function control mechanism for controlling operation in a selected one of a rotary drive mode and a hammering mode.
2. Description of the Related Art
A conventional power tool according to U.S. Pat. No. 5,458,206 includes a motor, a gear mechanism, a cylindrical housing, a drive spindle, and a function control mechanism. The gear mechanism is coupled to and is driven by the motor, and has a casing. The cylindrical housing is mounted on the casing of the gear mechanism. The drive spindle is mounted rotatably on the cylindrical housing, is coupled to and is driven rotatably by the gear mechanism, and is axially movable between front and rear limit positions relative to the cylindrical housing. The function control mechanism includes first and second ratchets, and a push ring. The first ratchet is mounted to rotate with the drive spindle. The second ratchet is slidable in the cylindrical housing from a first position to a second position. The push ring is disposed to abut against a rear surface of the second ratchet, and has a front surface that is formed with cam notches. The rear surface of the second ratchet is formed with cam knobs.
When the push ring is rotated so as to engage the cam notches and the cam knobs, this results in axial movement of the second ratchet to the first position. At this time, the first ratchet does not engage the second ratchet even when the drive spindle is moved axially to the rear limit position. As such, when a user presses a tool bit, which is secured on a front end of the drive spindle, against a workpiece, the drive spindle rotates without reciprocation.
When the push ring is rotated to disengage the cam notches and the cam knobs, this results in axial movement of the second ratchet to the second position. At this time, the first ratchet engages the second ratchet when the drive spindle is moved axially to the rear limit position. As such, when the user presses the tool bit against the workpiece, the drive spindle oscillates in axial movement, resulting in hammering action of the drive spindle.
The aforementioned conventional power tool achieves the purpose of switching between rotary drive and hammering modes of operation. However, the cam knobs of the second ratchet of the function control mechanism of the conventional power tool wear out easily due to frequent rotation of the push ring to engage and disengage the cam knobs and the cam notches, and the impact transmitted thereto during the hammering action of the drive spindle.
Therefore, the object of the present invention is to provide a power tool that has a function control mechanism, which can overcome the aforementioned drawback of the prior art.
According to the present invention, a power tool comprises a motor, a gear mechanism, a cylindrical housing, a drive spindle, and a function control mechanism. The gear mechanism is coupled to and driven by the motor, and has a casing. The cylindrical housing is mounted on the casing of the gear mechanism and is formed with a pair of diametrically opposite radial holes therethrough. The spindle mounting seat is disposed in the housing. The drive spindle is mounted rotatably on the spindle mounting seat, is coupled to and is driven rotatably by the gear mechanism, and is axially movable between front and rear limit positions relative to the spindle mounting seat. The function control mechanism includes a first ratchet, a second ratchet, a push ring, and a ring controller. The first ratchet is mounted to rotate with the drive spindle, and has front and rear surfaces. The rear surface of the first ratchet is formed with first ratchet teeth. The second ratchet is retained in the cylindrical housing, and has front and rear surfaces. The front surface of the second ratchet is formed with second ratchet teeth. The second ratchet is slidable in the cylindrical housing from a first position farther from the first ratchet to a second position closer to the first ratchet. The second ratchet teeth are disengaged from the first ratchet teeth when the second ratchet is in the first position. The second ratchet teeth are engaged with the first ratchet teeth when the second ratchet is in the second position and the drive spindle is in the rear limit position. The push ring is disposed in the cylindrical housing, abuts against the rear surface of the second ratchet, and has a pair of operable arms that extend radially and respectively through the radial holes in the cylindrical housing. The operable arms are movable between front and rear positions in the radial holes such that the second ratchet is in the first position when the operable arms are in the rear position, and such that the second ratchet is in the second position when the operable arms are in the front position. The ring controller is sleeved rotatably on the cylindrical housing, and is formed with a pair of circumferentially extending guide units. Each of the guide units is registered with a respective one of the radial holes in the cylindrical housing and is in sliding engagement with a respective one of the operable arms such that rotation of the ring controller relative to the cylindrical housing results in movement of the operable arms between the front and rear positions.